The spreading of liquid fertilizers, herbicides, and insecticides is accomplished with a spraying apparatus having a spray boom equipped with a plurality of spray nozzles. The liquid is pumped to the spray boom whereby the liquid is discharged under pressure through the nozzles. Controls, including vehicle speed sensors, flow meters for sensing the flow of liquid from the pump to the spray boom, and the flow control valves are used to vary the rate of the flow of the liquid through the nozzles in relation to the vehicle speed. These controls try to achieve a preset liquid spray spread density over a wide range of vehicle speeds.
A vehicle mounted liquid distributor disclosed by Herman in U.S. Pat. No. 3,782,634 has a spray bar system that utilizes several booms having sets of spray nozzles arranged to spread liquid uniformly over the same width. A pump draws liquid from a tank and discharges liquid through a flow meter and flow control valves to the separate spray booms. Each spray boom has a plurality of nozzles. Separate liquid flow control valves regulate liquid flow to booms. A control system responsive to vehicle speed and liquid flow rate is operable to regulate the flow control valves, thereby regulating the amount of liquid discharged by the nozzles. The control system does not include means to monitor the performance of the nozzles, nor means to change the liquid dispensing rate after initial setup of the control system.
The Herman liquid distributor apparatus has a limitation of reverse control. When one or more nozzles are plugged with foreign material, the flow control system is not aware of this condition. It can only sense the total flow to all of the nozzles with the use of its flow meter.
In normal operation of prior liquid distributors or sprayers, the nozzles have substantially the same sized orifices and dispense substantially the same amount of liquid onto the ground. These distributors measure the flow of the liquid with a single flow meter that measures the total flow in the system to all of the nozzles. The controllers for these systems do not know how the liquid flow is distributed or spread across the ground. The controllers simply divide the total liquid flow by the ground area covered to compute gallons per acre. If the measured gallons per acre is less than the desired gallons per acre, a servo-valve opens to increase the liquid pressure in the spray booms. This will increase the liquid flow. When one of the nozzles plugs, the flow in the system will decrease. The result is that the flow meter will slow down. The controller for the system will operate to increase the pressure to get the total flow of liquid back to its selected rate. The result is that the plugged nozzle is inoperable and the remaining nozzles are dispensing excess liquid. There is no warning to the operator of the plugged nozzle. The operator must visually observe the operation of all of the nozzles to insure their operation. In many distributors, all of the nozzles are not visible by the operator so liquid would not be dispensed over many acres without knowledge of an inoperative nozzle. The reverse control apparatus reacts to cover up the plugged malfunctioning nozzle.
Oligschlaeger discloses, in U.S. Pat. No. 3,877,645, a vehicle mounted liquid distributing apparatus having a pump for delivering liquid under pressure to a spray bar system. The flow of the liquid to the spray bar system is controlled in accordance with the ground speed of the vehicle to maintain a generally uniform preset spray spread density. The control includes a device for sensing the pressure of the liquid in the spray bar, a vehicle speed sensor, and an electrical circuit means responsive to the signals from the device for sensing pressure and vehicle speed sensor to control the rate of flow of liquid to the spray bar as a function of the square of the speed of the vehicle.
The flow control valves of the prior art liquid sprayers are known as servo-valves. These valves have valving members that operate over a fixed path of movement. In butterfly top valves, the path of movement operates over the same 90 degrees of rotation of the valve. Electromechanical end stops are required for these valves. One end stop determines the full open position of the valve and the other end stop the fully closed position of the valve. Over a period of use, the motion transmitting structure, including gears, will wear causing malfunctioning of the valve.
The application rate of the liquid sprayed cannot be readily varied in operation. The operator must stop the spraying operation and set a new rate in the controls for the liquid dispensing apparatus. This is inconvenient and requires considerable time.